Single and multiple sinewave modulation and demodulation techniques, apparatus, and communications systems

ABSTRACT

A method for generating a substantially sinusoidal waveform containing encoded digital data having one of a first value and a second value at selected phase angles θ n  comprises generating the waveform having an amplitude Y defined by a first function at phase angles lying outside of regions having a range Δθ beginning at each phase angle θ n , said first function being Y=sin θ; generating the waveform having an amplitude Y defined by the first function at phase angles lying inside the regions having a range of Δθ beginning at each phase angle θ n  where data of the first value is to be encoded; and generating the waveform having an amplitude Y defined by a second function at phase angles lying inside the regions having a range of Δθ associated with each phase angle θ n  where data of the second value is to be encoded, the second function being different from Y=sin θ.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to transmission of information throughmedia such as wire, cable, and radio-frequency propagation, bothterrestrial and satellite. More particularly, the present inventionrelates to a single and multiple sinewave modulation technique,apparatus for modulating and demodulating information according to themodulation technique, and communications systems employing themodulation technique.

2. The Prior Art

Digital data is often transferred from point to point by exploiting oneor more of the three characteristic properties of an AC signal:Amplitude, Frequency and Phase.

Some of the modulation methods using the amplitude property are OOK(On-Off Keying) and common AM (amplitude modulation). In OOK a data bitis represented by the presence or absence of a carrier. In AM data bitsare represented by a difference in the relative amplitude of the carrieror by using different tones representing the digital data to amplitudemodulate a carrier.

Typical modulation methods using the frequency property are FSK(Frequency Shift Keying and FM (frequency modulation). With FSK thebinary states of digital data are represented with abrupt frequencychanges between two predetermined fixed frequencies. In FM data bits arerepresented by a difference in the relative frequency of the carrier orby using different tones representing the digital data to frequencymodulate a carrier.

Phase modulation is also a common modulation method also but when usedalone is difficult to distinguish from FM. Recently more sophisticatedmodulation methods have evolved and have been exploited. As an example arelatively new and popular modulation method is QAM (QuadratureAmplitude Modulation), which uses a combination of amplitude and phasemodulation. There are several different variations of QAM depending onthe application.

Each of these modulation methods is viable, proven and used inappropriate communications applications. A few undesirablecharacteristics common to all of these modulation methods is they allrequire several cycles to transmit one bit and in doing so generatesignificant sidebands. These sidebands are necessary to extract theinformation from the carrier and take up significant bandwidth in thecommunications channel, requiring significant spacing between adjacentsignals.

BRIEF DESCRIPTION OF THE INVENTION

A modulation technique according to the present invention employs one ormore sinusoidal carriers. Digital data comprising a number of digitalbits are encoded within each half of the sinusoidal cycle. Eachindividual one of n bits is located at a predetermined phase angle ofthe cycle θ_(n). One digital representation (for example a “zero”) isrepresented by no change occurring in the amplitude Y of the sinusoidalwaveform at the phase angle θ_(n). The other digital representation (forexample a “one”) is represented by altering the sinusoidal waveform atthe phase angle θ_(n). Ax presently preferred, the sinusoidal waveformis altered by maintaining the amplitude Y=sin θn for a short interval Δθfollowing the phase angle θ_(n). Alternatively, the sinusoidal waveformcould be altered by increasing (or decreasing) the amplitude of thesinusoidal waveform and then maintaining the amplitude Y=sin θ_((n+Δθ))for the short interval Δθ following the phase angle θ_(n).

As presently preferred, but not necessary, every other bit is inverted(i.e., a “one” is inverted to a “zero” and a “zero” is inverted to a“one”). Either or both of the number of bits n and the phase anglesphase angle θ_(n) may be adaptively altered or may be selectivelyaltered for a number of purposes.

In embodiments where a plurality of sinusoidal carriers are employed,the sinusoidal carriers may be related in frequency such that they maybe generated having a phase relationship characterized by all of thecarriers simultaneously being at zero degrees (sin θ=0) periodically.

A demodulation technique according to the present invention detects themodulated carrier and retrieves the digital data by examining it todetermine whether the sinusoidal function of the carrier has beenaltered at an interval Δθ following each phase angle θ_(n). For,example, if the carrier has been modulated by maintaining the amplitudeY=sin=θ_(n) for a short interval Δθ following the phase angle θ_(n), themodulated carrier is examined to determine if Y=sin θn during theinterval Δθ following the phase angle On or whether the amplitude hasbeen following the function Y=sin θ during the interval Δθ followingeach phase angle θ_(n). Such examination may be accomplished, forexample, by mixing the detected sinusoidal carrier with a referencesinusoidal signal having the same frequency and phase as the carrier todetect phase differences between the reference sinusoidal signal and themodulated carrier, or by performing fast-fourier-transform (FFT)analysis on the modulated carrier. The digital data may then be bufferedor otherwise processed and utilized as known in the digital data art.

An exemplary modulation apparatus according to the present invention maybe employed to digitally generate the modulated carrier. A counter maybe used to drive a digital-to-analog (D/A) converter through asine-function lookup table as is known in the art to generate asinusoidal output voltage from the D/A converter. The output of thecounter at points in time representing θ_(n) may be latched into thesine-function lookup table if it is desired to maintain the output ofthe D/A converter at the value Y=sin θ during the interval Δθ. At theend of the interval Δθ, the latch is released and the then-current-countoutput of the counter is presented to the lookup table. According to oneembodiment of the invention, the bit rate is adaptable.

One exemplary demodulation apparatus according to the present inventionmay be employed to extract the digital information from the modulatedcarrier. The modulated carrier is used to generate a referencesinusoidal signal having the same frequency and phase as the modulatedcarrier. The modulated carrier and the reference sinusoidal signal aremixed in a double-balanced mixer. Digital circuitry examines the outputof the mixer during a time window including and just following theinterval Δθ for a signal indicating a phase change between the modulatedcarrier and the reference sinusoidal signal. The sensed signals becomethe digital output stream of the demodulator.

Another exemplary demodulation apparatus uses optical techniques toextract digital information from the modulated carrier. These techniquesexploit the fact that the brightness of a LED will be higher during thepresence of an encoded bit.

One communications system according to the present invention employs amodulator to insert at least one modulated carrier according to thepresent invention onto one end of a telephone line or other wire-paircommunications line. Preferably, a plurality of such modulated carriers,separated in frequency by a guard-band amount, are injected into theline. A demodulator is coupled to the other end of the telephone line orother wire-pair communications line. According to one embodiment of theinvention, a modulator and the demodulator may be located at each end ofthe line and the communications may be two-way communications. Accordingto another embodiment of the invention, the modulator and thedemodulator may negotiate a bit rate to be used in the communications.

Another communications system according to the present invention employsa modulator to insert at least one modulated carrier according to thepresent invention onto a power distribution line. Preferably, aplurality of such modulated carriers, separated in frequency by aguard-band amount, are injected into the line. A demodulator is coupledto the power distribution line at a customer location such as a home orbusiness at, for example, a conventional duplex outlet. According to oneembodiment of the invention, the communications may be two-waycommunications. According to another embodiment of the invention, themodulator and the demodulator may negotiate a bit rate to be used in thecommunications. According to yet another embodiment of the invention thecommunications system may be used by a power utility to regulate loadsduring periods of high load demand by selectively switching appliancesand lighting circuits at the customer location.

Another communications system according to the present invention employsa modulator to insert at least one modulated carrier according to thepresent invention onto one end of a coaxial-cable communications line.The modulated carriers may be up-converted in frequency prior to beinginserted onto the coaxial cable line. Preferably, a plurality of suchmodulated carriers, separated in frequency by a guard-band amount, areinserted into the line. A demodulator is coupled to the other end of thecoaxial cable communications line. According to one embodiment of theinvention, a modulator and the demodulator may be located at each end ofthe line and the communications may be two way communications. Accordingto another embodiment of the invention, the modulator and thedemodulator may negotiate a bit rate to be used in the communications.

Another communications system according to the present invention employsa modulator to generate at least one modulated carrier according to thepresent invention and to further modulate a radio-frequency (RF) carrierwith the at least one modulated carrier to form a wireless RF signal.The modulated carriers may be up-converted in frequency prior to beingRF modulated. Preferably, a plurality of such modulated carriers,separated in frequency by a guard-band amount, are RF modulated. The RFmodulated signal is then transmitted. The transmitted RF modulatedsignal is then detected by a terrestrial RF receiver. A demodulator iscoupled to the terrestrial RF receiver. According to one embodiment ofthe invention, the communications may be two-way communications.According to another embodiment of the invention, the modulator and thedemodulator may negotiate a bit rate to be used in the communications.

Another communications system according to the present invention employsa modulator to generate at least one modulated carrier according to thepresent invention and to further modulate a radio-frequency (RF) carrierwith the at least one modulated carrier to form a wireless RF signal.The modulated carriers may be up-converted in frequency prior to beingRF modulated. Preferably, a plurality of such modulated carriers,separated in frequency by a guard-band amount, are RF modulated. The RFmodulated signal is then transmitted to an earth-orbiting or othersatellite or spacecraft. A demodulator is coupled to the RF receiver inthe earth-orbiting or other satellite or spacecraft. The earth-orbitingor other satellite or spacecraft may then retransmit the RF signal toanother RF receiver or may demodulate it for local use. According to oneembodiment of the invention, the communications may be two-waycommunications. According to another embodiment of the invention, themodulator and the demodulator may negotiate a bit rate to be used in thecommunications.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

FIG. 1A is a diagram illustrating an exemplary single sinusoidal carriermodulated according to the techniques of the present invention.

FIG. 1B is a graph of voltage vs. time of both a single cycle of asinewave carrier modulated according to the techniques of the presentinvention and of exemplary data detected from that carrier.

FIG. 2 is a diagram illustrating a plurality of sinusoidal carriers thatmay be modulated according to the techniques of the present invention.

FIG. 3 is a block diagram of an illustrative modulator circuit forgenerating a modulated sinusoidal carrier according to the techniques ofthe present invention.

FIGS. 4A and 4B are, respectively, block diagrams of a frequency upconverter and down converter that may be used in communications systemsaccording to the present invention.

FIG. 5A is a block diagram of a plurality of illustrative modulatorcircuits, each for generating a modulated sinusoidal carrier, whoseoutputs are mixed together according to the techniques of the presentinvention.

FIG. 5B is a block diagram of a system including a plurality ofillustrative modulator circuits, each for generating a modulatedsinusoidal carrier, whose outputs are mixed together according to thetechniques of the present invention.

FIG. 6 is a block diagram of an illustrative demodulator circuit forextracting the information from a modulated sinusoidal carrier accordingto the techniques of the present invention.

FIG. 7 is a block diagram of a plurality of illustrative demodulatorcircuits, each for demodulating a modulated sinusoidal carrier, whoseoutputs are combined into an output data stream according to thetechniques of the present invention.

FIG. 8 is a block diagram of an optical demodulator circuit that may beused in accordance with the present invention.

FIG. 9A is a block diagram illustrating a communications systemaccording to the present invention operating over a wire-paircommunications line such as a telephone line including a modulator oneach end of a telephone line to insert at least one modulated carrieraccording to the present invention onto one end of the wire-paircommunications line and a demodulator coupled to each end of thetelephone line or other wire-pair communications line for performing twoway communications.

FIG. 9B is a block diagram illustrating a communications systemaccording to the present invention operating over an electrical-powerdistribution line including a modulator coupled to the electrical-powerdistribution line to insert at least one modulated carrier according tothe present invention onto one end of the electrical-power distributionline and a demodulator coupled to each end of the electrical-powerdistribution line for performing two way communications.

FIG. 10 is a block diagram illustrating communications system for acoaxial-cable communications line according to the present inventionemploying a modulator to insert at least one modulated carrier accordingto the present invention onto each end of the coaxial-cablecommunications line and a demodulator coupled to each end of the coaxialcable communications line.

FIG. 11 is a block diagram illustrating another communications systemaccording to the present invention employing on each end a modulator togenerate at least one modulated carrier according to the presentinvention and to further modulate a radio-frequency (RF) carrier withthe at least one modulated carrier to form a wireless RF signal and aterrestrial RF receiver coupled to a demodulator.

FIG. 12 is a block diagram illustrating another communications systemaccording to the present invention employing on each end a modulator togenerate at least one modulated carrier according to the presentinvention and to further modulate a radio-frequency (RF) carrier withthe at least one modulated carrier to form a wireless RF signaltransmitted to an earth-orbiting or other satellite or spacecraft and ademodulator coupled to the RF receiver in the earth-orbiting or othersatellite or spacecraft.

FIG. 13 is a block diagram illustrating how digital signal processingtechniques may be used in a communications system according to thepresent invention to produce at least one modulated sinusoidal carrieras shown in FIG. 2.

FIG. 14 is a block diagram illustrating how digital signal processingtechniques may be used in a communications system according to thepresent invention to demodulate at least one modulated sinusoidalcarrier.

FIG. 15 is a block diagram illustrating how a communications systemaccording to the present invention can be used in conjunction with anexisting modem protocol.

FIG. 16 is a block diagram that depicts an illustrative embodiment of amulti-frequency sinewave receiver.

DETAILED DESCRIPTION OF THE INVENTION

Those of ordinary skill in the art will realize that the followingdescription of the present invention is illustrative only and not in anyway limiting. Other embodiments of the invention will readily suggestthemselves to such skilled persons.

Referring first to FIG. 1A is a diagram illustrates an exemplary singlesinusoidal carrier 10 modulated according to the techniques of thepresent invention. A positive half cycle of a sinusoidal wave is shownin FIG. 1A. The x-axis of FIG. 1A is the phase angle of the sinusoidalcarrier 10 from 0° through 180° and the y-axis of FIG. 1A is theinstantaneous amplitude of sinusoidal carrier 10 normalized to a peakvalue of 1 at a phase angle of 90° as is known in the art. Persons ofordinary skill in the art will appreciate from an examination of FIG. 1Ahow the encoding of the second half cycle of the sinusoidal carrier 10from 180° through 360° is performed.

According to then present invention n digital bits are encoded withineach half of the sinusoidal cycle. Each individual one of n bits islocated at a predetermined phase angle of the cycle On. One digitalrepresentation (for example a “zero”) is represented by no changeoccurring in the amplitude Y of the sinusoidal waveform at the phaseangle θ_(n). The other digital representation (for example a “one”) isrepresented by altering the sinusoidal waveform at the phase angleθ_(n). As presently preferred, the sinusoidal waveform is altered bymaintaining the amplitude Y=sin θ_(n) for a short interval Δθ followingthe phase angle θ_(n). As presently preferred, every other bit isinverted (i.e., a “one” is inverted to a “zero” and a “zero” is invertedto a “one”). Persons of ordinary skill in the art will appreciate thatalterations of the sinusoidal carrier other than maintaining the voltageconstant during the interval Δθ following the phase angle θ_(n) arepossible in accordance with the teachings of the present invention. Forexample, the sinusoidal waveform could be altered by increasing (ordecreasing) the amplitude of the sinusoidal waveform and thenmaintaining the amplitude Y=sin θ_((n+Δθ)) for the short interval Δθfollowing the phase angle θ_(n). Combinations of these two techniquescould be employed according to the present invention.

In FIG. 1A, n is selected to be 4 solely for purposes of ease inillustrating the present invention. The present invention is not limitedto encoding 4 digital bits per half cycle of sinusoidal carrier 10 andpersons of ordinary skill in the art will observe that other numbers ofbits may be encoded per half cycle of sinusoidal carrier 10. Thelocations of the encoded bits on the carrier 10 are shown at phaseangles θ₁, θ₂, θ₂, and θ₄, respectively. These bit positions are shownin FIG. 1A symmetrically located. Such positioning, while convenient forperforming the demodulation of the signal, is not necessary inaccordance with the present invention.

For purposes of FIG. 1A, a “zero” data value is represented by no changeoccurring in the amplitude Y of the sinusoidal waveform and a “one”) isrepresented by altering the amplitude Y of the sinusoidal waveform. Inthe example of FIG. 1A, a modulation technique is used wherein everyother bit is inverted (i.e., a “one” is inverted to a “zero” and a“zero” is inverted to a “one”). Therefore, bits 2 and 4 are showninverted in FIG. 1A. While this modulation technique (inverting everyother bit) is presently preferred, persons of ordinary skill in the artwill appreciate that this is not necessary for practicing the presentinvention.

FIG. 1A illustrates encoding the four-bit sequence 1000, in which bits 2and 4 are inverted so that the encoded sequence is shown as 1101 encodedin the first half cycle of sinusoidal carrier 10. Thus, starting atphase angle θ₁ and for a short interval Δθ following the phase angle θ₁,the sin θ function becomes discontinuous and the Y value is heldconstant at the value Y=sin θ₁. At the end of the interval Δθ, the Yvalue jumps up to Y=sin [θ₁+Δθ]. Similarly, starting at phase angle θ₂and for a short interval Δθ following the phase angle θ₂, the sinefunction becomes discontinuous and the Y value of the function is heldconstant at the value Y=sin θ₁, since an inverted “0” (a “1”) is beingencoded. At the end of the interval Δθ, the Y value rises to Y=sin[θ₂+Δθ]. There is no interruption of the sin θ function at the angleinterval Δθ immediately following phase angle θ₃, since a zero is beingencoded at that location. Finally, starting at phase angle θ₄ and for ashort interval Δθ following the phase angle θ₄, the Y value of thefunction is held constant at the value Y=sin θ₄, since an inverted “0”(a “1”) is being encoded. At the end of the interval Δθ, the Y valuefalls to Y=sin [θ₂+Δθ].

From an examination of the first and fourth encoded bits, persons ofordinary skill in the art will observe that the portions of the waveformat encoded bits at phase angles θ₁ and θ₄ are not symmetrical. At phaseangles of less than 90° the rise of the Y value is delayed and at phaseangles of greater than 90° the fall of the Y value is delayed. In bothcases, however, the abrupt change in the Y value (ΔY) occurs at the endof the interval Δθ, during which Y has been constant. This is the abruptchange that will be sensed by the detector to demodulate the signal andextract the digital information. As previously noted, persons ofordinary skill in the art will appreciate that at phase angles greaterthan 90° the abrupt change could be caused to occur at the beginning ofthe interval Δθ or that the abrupt change in amplitude could be at thebeginning of the interval at phase angles less than 90° and at the endof the interval at phase angles greater than 90°.

A central portion of the sinusoidal carrier 10 symmetrically locatedaround 90° is identified in FIG. 1A by diagonal hatching. It is believedthat, as a practical matter, there is some range of phase anglessymmetrically located around 90° for which the abrupt change ΔY in thevalue of Y will be difficult or impossible to detect since dsin θ/dθ(i.e., cos θ) approaches zero as θ approaches 90° from both directions.This can be seen by comparing ΔY1 and ΔY2 and noting that the latter isa smaller amplitude change. It is therefore presently preferred to avoidlocating the bit positions near the phase angle θ=90°. The size of thisexclusion zone will depend on factors such as, but not limited to, thedetection scheme employed, the transmission medium employed, and theambient noise level in the transmission medium.

Persons of ordinary skill in the art will appreciate that variations ofthe modulation technique disclosed with reference to FIG. 1A arepossible without departing from the concepts of the present invention.For example, this aspect of the invention has been disclosed withrespect to use of a constant phase-angle interval Δθ to produce aresultant abrupt change in the value of abrupt change in the voltagevalue of Y. It is also contemplated to use a constant abrupt change inthe voltage value ΔY with the result that the magnitude of thephase-angle interval Δθ will depend on the angular position at which thechange in the voltage value ΔY is desired. In addition, the voltageduring the interval Δθ in the example of FIG. 1A is held constant at thevalue Y=sin θ_(n), but other functions could be employed.

Referring now to FIG. 1B, a graph of voltage vs. time of both a singlecycle of a sinewave carrier modulated according to the techniques of thepresent invention and of exemplary data detected from that carrier ispresented. In the upper trace, a single cycle of a sinewave carrier isshown modulated with four bits per half cycle. In the upper trace, arepresentation is shown of the voltage that would be detected from thatcarrier using the techniques of the present invention. The absence ofencoded data in the region symmetrical about 90° is noted.

Referring now to FIG. 2, a diagram illustrates another aspect of thepresent invention in which a plurality of sinusoidal carriers may bemodulated with different digital data in the same communications channelaccording to the techniques of the present invention. In theillustrative example of FIG. 2, it may be seen that portions of sevensinusoidal carriers are shown within a 40 mS “frame” wherein all of thecarriers are at a phase angle of zero at the beginning of each frame.Persons of ordinary skill in the art will understand that this can bereadily accomplished by selecting carrier frequencies that aremathematically related in frequency. In the illustrative example of FIG.2, carrier frequencies starting at 400 Hz and spaced apart by 25 Hz(i.e., 250 Hz, 275 Hz, 300 Hz, 325 Hz, 350 Hz, 375 Hz, and 400 Hz havebeen selected. As shown in the particular example illustrated in FIG. 2,the use of 16 bits per cycle results in a data rate of 1,456 bits perframe or 36,400 bits per cycle.

As may be seen from FIG. 2, the carriers are mathematically related suchthat ten complete cycles of a first carrier, eleven complete cycles of asecond carrier, twelve complete cycles of a third carrier, thirteencomplete cycles of a fourth carrier, fourteen complete cycles of a fifthcarrier, fifteen complete cycles of a sixth carrier, and sixteencomplete cycles of a seventh carrier are contained within the frame.Such framing, wherein all of the carriers are at a phase angle of zeroat the beginning of each frame, is not necessary for practicing thepresent invention using multiple carriers, but it may be advantageouslyemployed for data recovery and other synchronization activities in acommunications system according to the present invention. For example,the frame-start phasing illustrated in FIG. 2 may be used forsynchronization purposes etc.

This multiple-carrier aspect of the present invention can be employed toexpand the total bandwidth that may be available in a givencommunications channel. For example, as will be disclosed herein, thebandwidth of a typical twisted-pair telephone line is about 3 KHz.According to the present invention, a plurality of sinusoidal carriersmay each be spaced about 50-100 Hz apart in frequency within thisfrequency range and transmitted over the same telephone line. This canbe used to significantly increase the usable bandwidth in anycommunication channel in which the present invention is employed.Persons of ordinary skill in the art will recognize from this disclosurethat other frequency separations will be useable at other frequencies.For example, at a frequency of about 100 MHz, a plurality of sinusoidalcarriers may be spaced apart from one another by about 500 KHz. Personsof ordinary skill in the art will understand that, in any given systemrealized according to the present invention, the required carrierspacing is simply that necessary to avoid interference from adjacentcarrier frequencies during detection and will depend on the frequencyrange utilized, as well as the detection techniques that are employed.

According to another aspect of the present invention, securecommunications may be accomplished by selecting combinations of two ormore carrier frequencies. Authorized transmissions in such a system maybe identified by receivers configured to detect the presence of theselected combination of carrier frequencies. According to one aspect ofthe present invention, communications systems may be adaptive and mayuse information sent over a control channel or frequency shifts detectedby the receiver to shift the frequency of one or more carriers forpurposes such as noise avoidance or minimization, security purposes,enabling multiple modes of communications, identifying messages intendedfor selected receivers, identifying events, etc. The purposes for whichthis aspect of the invention may be implemented will vary widely and arelargely a matter of design choice.

Referring now to FIG. 3, a block diagram depicts an illustrativemodulator circuit for generating a modulated sinusoidal carrieraccording to the techniques of the present invention. The modulator ofFIG. 3 is only illustrative, and persons of ordinary skill in the artwill recognize that other schemes, such as a programmed microprocessorand digital signal processing (DSP) techniques, state machines, etc.,may be employed to perform this function.

Generation of a sinusoidal voltage by use of a sine-function lookuptable driving a D/A converter is known. The phase angles from 0° to 360°are quantized to a number of discrete values. A multi-bit countercontinuously counts through these discrete values at a constant clockrate. The output of the multibit counter addresses the sine-functionlookup table that provides the digital encoded sine-function value foreach quantized phase angle. The D/A converter outputs a voltageproportional to the sine of the discrete phase angle at the input of thelookup table.

The two variables are the phase-angle resolution and the resolution ofthe A/D converter. In the illustrative modulator circuit of FIG. 3, thephase angle range of 0° to 360° is shown resolved to 9 bits, or one partin 512, making each increment of θ=0.703125°. Persons of ordinary skillin the art will appreciate that other resolutions could be employed,although the number of bits that may be encoded in a half cycle of thesinusoidal carrier may be limited for smaller resolutions. For example,using a 9-bit resolution of θ, each half cycle is resolved into 256discrete angles. It is believed that a practical limit of 64 bits may beachievable using this angular resolution.

Similarly, the resolution of the D/A converter should be selected sothat the step size is small enough to provide a relatively low amount ofdistortion in an unmodulated sinusoidal carrier generated therefrom. Itis presently preferred that the resolution of the D/A converter be atabout 10 bits. Persons of ordinary skill in the art will appreciate thatthe resolution of the D/A converter will affect the ability to use FFTdemodulating techniques, since it is desirable that the smallestcontemplated ΔY be significantly larger than the D/A step size.

Discrete logic elements are depicted in FIG. 3. Persons of ordinaryskill in the art will appreciate that these elements can be fabricatedusing different technologies such as bipolar technology, CMOStechnology, etc., and that logic families such as TTL, ECL, etc., may bechosen depending on the speed requirements dictated by the operatingfrequencies for which the circuits are designed. Further, such skilledpersons will understand that these elements may be integrated onto asingle integrated circuit, or that these elements could be programmedinto a programmable integrated circuit such as a field programmable gatearray or that the logic functions performed could be realized as a statemachine.

In FIG. 3, clock generator 20 is shown driving 9-bit binary counter 22.The 9-bit count output from counter 22 is provided through delay element24 to latch 26. Latch 26 is configured to be transparent while its clockinput is low and to latch at its output the 9-bit value appearing on itsinput when its clock input becomes high. The output of latch 26 is usedto drive sine lookup table 28. The output of sine lookup table 28 drivesD/A converter 30. D/A converter 30 is shown in FIG. 3 having aresolution of 10 bits in FIG. 3, but from this disclosure, persons ofordinary skill in the art will understand that different resolutions maybe employed. The modulated sinusoidal carrier of FIG. 1A appears at theoutput of D/A converter 30. Persons of ordinary skill in the art willappreciate that, in the 9-bit counter example of FIG. 3, the frequencyof clock generator 20 is selected to be 512 times the desired sinusoidalcarrier frequency.

Modulation may be applied to the sinusoidal carrier by temporarilyfreezing the input to sine lookup table 28 for a number of clock pulseswhose periods together equal the desired time interval corresponding toΔθ. Experienced digital designers will appreciate that there arenumerous ways in which to accomplish this.

One illustrative example of an extremely flexible method for performingthis modulation technique is shown in FIG. 3 using non-volatile memory32. Non-volatile memory 32 may be any sort of non-volatile memory, suchas a mask ROM, PROM, EPROM, EEPROM, flash memory, etc.

The 9-bit count output from counter 22 is also provided to the 9 leastsignificant bits of non-volatile memory 32, which then has one locationcorresponding to each discrete phase angle into which the sinusoidalcarrier is resolved. In the circuit of FIG. 3, memory locations innon-volatile memory 32 corresponding to phase angles in the ranges[θ₁+Δθ], [θ₂+Δθ], [θ₃+Δθ], and [θ₄+Δθ] contain the value “1” and memorylocations in non-volatile memory 30 corresponding to phase anglesoutside of these ranges contain the value “0”.

The data to be encoded is transferred to data input register 34. Datainput register 34 is a parallel-in serial-out register. Data inputregister 34 is loaded with n bits of data, n being the number of bitpositions that may be encoded into a half cycle of the sinusoidalcarrier. Data input register 34 is falling-edge clocked by the dataoutput of non-volatile memory 32. Prior to the first clock pulse, thefirst data bit appears at the serial output of data input register 34.When the output count of 9-bit counter 22 reaches the valuecorresponding to the phase angle location of the first data bit to beencoded, the output of non-volatile memory 30 presents a “1” value aspreviously disclosed. If the value of the first data bit appearing atthe serial output of data input register 34 is also a “1” value, theoutput of AND gate 36 becomes true (a value of “1”). This latches thecount of 9 bit counter 22 at the output of latch 24, causing the outputof D/A converter 30 to remain constant. From an examination of FIG. 3,persons of ordinary skill in the art will appreciate that delay element24 is interposed in the output path of counter 22 to allow the output ofnonvolatile memory 32 and the output of AND gate 36 to settle prior tothe new count reaching latch 26.

During this time, 9-bit counter 22 continues to count and its outputsequentially addresses the contents of non-volatile memory 32. So longas the output of non-volatile memory 32 presents a “1” value to AND gate36, the output of latch 26 remains latched. When the output ofnon-volatile memory 32 drops to a “0” value, AND gate 36 releases latch26 and the current output count of 9-bit counter 22 is presented tolookup table 28, causing the output of D/A converter 30 to immediatelyrise (or fall) to the value of Y=sin θ for the current value of 0represented by the current output count of 9-bit counter 22.

As previously noted, there are numerous ways in which to modulate thesinusoidal carrier by temporarily freezing the input to sine lookuptable 28 for a number of clock pulses whose periods together equal thedesired time interval corresponding to Δθ. One advantage of employingthe scheme shown in FIG. 3 using non-volatile memory 32 is that thepositions of the data bits at phase angles θ₁, θ₂, θ₂, and θ₄, and theintervals Δθ can be collectively or individually adjusted simply byprogramming the contents of non-volatile memory 32. For, example, aspreviously disclosed herein, the lengths of intervals Δθ can beindividually adjusted in order to cause substantially-equal ΔY changesfor representing “1” value bits.

Another advantage obtained by employing non-volatile memory 32, as shownin FIG. 3, is that the bit rate of the modulation may be selectivelyaltered. Non-volatile memory 32 is shown including higher-order-bitaddress inputs 38 and 40, controlled by bit-rate controller 42. Thisexample allows addressing four separate segments of non-volatile memory32. Each segment may be programmed with data representing differentnumbers of bit-encoding phase angles, different intervals for Δθ, ordifferent combinations of both parameters.

As will be appreciated by persons of ordinary skill in the art, bit ratecontroller 42 may be configured to adaptively and dynamically alter thebit rate and/or the intervals for Δθ modulation in response to changingconditions within the communication channel in which the modulator ofthe present invention is employed. As a non-limiting example, thistechnique could be used to negotiate connection speed over twisted-pairtelephone lines as is done in present-day dial-up modems. Similarly,this technique may be employed to alter the bit rate of the modulationtechnique of the present invention in any communications channel inwhich it is employed to compensate for dynamically-changing conditions,such as noise, etc., in the communications channel.

As will also be appreciated by persons of ordinary skill in the art, thebit rate and/or one or more of the phase-angle positions for Δθmodulation can be switched using bit-rate controller 42 and additionaladdress lines to access other memory locations for other purposes. Suchpurposes include identifying synchronization frames, identifying packetheaders for use in IP or other packet protocol systems, or identifyingother events or conditions. In this manner, detection of“out-of-position” bits in received carriers can be assigned meaningssuch as identifying events, providing additional data, etc. Thesemeanings may change depending on where in a “frame” this activityoccurs.

The nature of bit-rate controller 42 will depend to a large extent onthe nature and architecture of the system in which the modulator isdisposed and on the conditions that will be used to alter the bit rateor the bit phase-angle positions. As an example, bit-rate controller 42could be configured as a state machine, a microcontroller or amicroprocessor. Configuration of the state machine and/or programming ofthe microcontroller or microprocessor will, of course, depend on theexact process that is being performed and is a routine task for a personof ordinary skill in the art.

As a general example, however, bit-rate controller may be conditioned tosense the presence of a condition, request, interrupt, event, or thelike, and assert an address to a location in memory 32 that contains thedata to produce the number of bits desired and/or set one or more bitpositions at desired phase angles of the sinusoidal carrier to effectthe specific response to the condition, request, interrupt, event, orthe like. If additional data is being encoded, one phase-angle settingof the bit positions in the sinusoidal carrier can represent a firstdigital state (e.g., a “zero”) and a second phase-angle setting of thebit positions in the sinusoidal carrier can represent a second digitalstate (e.g., a “one”).

A receiver for demodulating the modulated sinewaves of the presentinvention may be conditioned to detect one or more “out-of-position”bits in one or more carriers and perform different actions based uponthe detection and the meanings assigned to the condition. One advantageof employing this technique according to the present invention is thatthis may be accomplished while still utilizing the detected data,meaning that this increase in function may be obtained without degradingthe bandwidth of the communications channel. For example, a carrierpresenting “out-of-position” encoded bits could be used to signal thatthe system is about to increase or decrease the number of carriers inthe channel. Persons of ordinary skill in the art will understand thatthe uses for this additional intelligence capability of the presentinvention are virtually limitless and are adaptable to the particularconfiguration and end use of the system in which they are employed.

The output of D/A converter 30 may be buffered, and/or mixed withoutputs of D/A converters from other modulators as disclosed herein, andmay be otherwise further conditioned, e.g., by further modulation orfrequency conversion as necessary to prepare signals for insertion intovarious communication channels. This aspect of the present invention isillustrated in FIGS. 4A and 4B, to which attention is now drawn.

FIG. 4A is a block diagram of a frequency up converter that may be usedfor preparing modulated carriers for transmission in communicationssystems according to the present invention. Local oscillator 40 drivesone input of balanced RF mixer 42. A modulated sinewave carrier set ispresented to the other input of balanced RF mixer 40. The output ofbalanced RF mixer 40 is passed through bandpass filter 44. Thearrangement of FIG. 4A for use as an upconverter is well known in the RFart.

FIG. 4B is a block diagram of a frequency down converter that may beused for downconverting received modulated carrier signals incommunications systems according to the present invention. As in FIG.4A, local oscillator 40 drives one input of balanced RF mixer 42. Thereceived RF input presented to the other input of balanced RF mixer 40through bandpass filter 46. The output of balanced RF mixer 40 is passedto a detector of the type disclosed herein. The arrangement of FIG. 4Bfor use as a downconverter is also well known in the RF art.

As an example, of the use of upconverters and downconverters in thecontext of the present invention, carriers at frequencies in the lMHzrange can be frequency converted to the 100 MHz range for transmissionover coaxial cable communications channels, and 100 MHz range can befrequency converted to the gigahertz range for transmission overmicrowave-link communications channels such as terrestrialpoint-to-point links or satellite links. Techniques for such signalconditioning and frequency conversion are well known in the art.

Another aspect of the invention is illustrated in FIG. 5A, which is ablock diagram of a plurality of illustrative modulator circuits, eachfor generating a modulated sinusoidal carrier, whose outputs are mixedtogether according to the techniques of the present invention. Modulatorcircuits 50-1, 50-2, 50-3, and 50-4, may all be configured asillustrated in FIG. 3 or may be otherwise configured. Themodulated-sinusoidal-carrier output of each modulator is fed to mixingcircuit 52. Mixing circuit 52 may be configured as simply as a summingamplifier as is known in the art or may be otherwise configured.

The output of mixing circuit 52 is a composite waveform containing allof the individual modulated sinusoidal carriers from modulator circuits50-1, 50-2, 50-3, and 50-4. The composite waveform at the output ofmixing circuit 52 may be otherwise further conditioned, e.g., by furthermodulation or frequency conversion as necessary to prepare signals forinsertion into various communication channels. Techniques for suchsignal conditioning and conversion are well known in the art.

Referring now to FIG. 5B, a block diagram shows a system 60 including aplurality of illustrative modulator circuits, each for generating amodulated sinusoidal carrier, whose outputs are mixed together accordingto the techniques of the present invention. The multi-frequencyelemental phase shift data transmitter described here is one of manyrealizations of a method to use elemental phase shifts of a carrier(s)to convey digital data.

A controller 62 provides the supervision and control of the buffer 64stores the data that comes in from its source. The input data is clockedin from the outside source. It could be serial or parallel in format.The data buffer 64 under the supervision of the controller 62 outputs aspecific data bit just at the right time for the assertion (if a one) orde-assertion (if the bit is a zero) of a elemental phase change asdescribed above.

A plurality of sequencer state machines 66-1 through 66-6 as the nameimplies, are each state machines that, when clocked, sequence throughthe address outputs to drive a plurality of corresponding sinewavelook-up tables (LUTs) 68-1 through 68-6, respectively. Persons ofordinary skill in the art will appreciate that the number of suchsequencer state machines used in an actual realization of the presentinvention is arbitrary and six are shown only as an illustrativeexample. Each of the state machines 66-1 through 66-6 are used togenerate the sinewave carriers according to the principles of thepresent invention and may be configured, for example, to perform theprocess disclosed with respect to FIG. 3 or an equivalent process thatgenerates the modulated sinewave carrier of FIGS. 1A and 1B.

Sinewave LUTs 68-1 through 68-6 are fixed preprogrammed memories similarto a Read Only Memory (ROM). These memories are each programmed so thatfor each input address location the data register holds a specificdigital value of the amplitude of a sinewave at a specific phase orangle of the wave location. In common implementations as the addressesare sequentially stimulated the data output outputs a digitalrepresentation of a sine wave. The peak amplitude is fixed and thefrequency of sinewave directly corresponds to the rate the addresses aresequenced and the number of address steps that make up a complete wave.

The sequencer state machines 66-1 through 66-6 each have three inputs:clock, data and reset. The clock causes the sequencer state machines66-1 through 66-6 to sequence through the addresses to produce asinewave signal from the LUTs 68-1 through 68-6. When a data bit ispresent and at the right phase location of the sinewave the sequencerwill cause its associated LUT to delay its output cause a elementalphase change in its output. The reset, when asserted, brings eachsequencer state machine back to a known state.

The LUTs 68-1 through 68-6 are each essentially a fixed preprogrammedmemory similar to a Read Only Memory (ROM). This memory is programmed sothat for each input address location the data register holds a specificdigital value of the amplitude of a sinewave at a specific phase orangle of the wave location. In common implementations as the addressesare sequentially stimulated the data output outputs a digitalrepresentation of a sine wave. The peak amplitude is fixed and thefrequency of sinewave directly corresponds to the rate the addresses aresequenced and the number of address steps that make up a complete wave.

There are numerous schemes that may be employed to distribute the datafrom data buffer 64 to distribute the data to sequencer state machines66-1 through 66-6. As previously noted, the data rate for each ofsequencer state machines 66-1 through 66-6 will be different.

One exemplary way to distribute the data is to distribute each bit inturn to the one of sequencer state machines 66-1 through 66-6 that isgoing to encode the next bit. This method may be referred to herein as“streaming” and has the advantage that it requires no reassembly of thedata at the receiver since the data is in the form of a simple serialdata stream. This timing may be derived as a matter of simplemathematics once a system design is specified and the number andfrequencies of the carriers is determined. The details of gating of thedata to the appropriate one of sequencer state machines 66-1 through66-6 from a data distributor according to a known sequence is a matterof routine digital circuit design. With reference again to FIG. 2 as anexample, and assuming that 4 bits will be encoded into each half cycleof each sinewave carrier, the absolute position in time for each angularposition of phase angles θ₁, θ₂, θ₂, and θ₄ can be easily calculated foreach sinewave carrier in a single frame. Each of these times, and theone of the sinewave carriers with which it is associated, may be used bythe controller 62 to distribute the next data bit to the appropriate oneof sequencer state machines 66-1 through 66-6.

Another exemplary way to distribute the data is, for each frame, toallocate to each one of sequencer state machines 66-1 through 66-6 ablock of data having a number of bits equal to the number of bits thatsequencer will encode in the current frame. This information is knownonce a system design is specified and the number and frequencies of thecarriers is determined. In the example of FIG. 2, Table 1 shows thenumber of bits that will be used per frame for each carrier. CYCLES PERBITS PER FREQUENCY FRAME FRAME 250 Hz 10 160 275 Hz 11 176 300 Hz 12 192325 Hz 13 208 350 Hz 14 224 375 Hz 15 240 400 Hz 16 256

As will be appreciated by persons of ordinary skill in the art,depending on the complexity of the data distributing on the encodingend, this data distribution scheme might be constrained in that it maynot be possible to accommodate extremely fast data rates on thereceiving end because the data distributor has to wait for the datablocks of each carrier to be filled prior to the blocks being ready forrelease.

The outputs of the LUTs 68-1 through 68-6 are presented to D/Aconverters 70- through 70-6, respectively. The D/A converters 70-through 70-6 linearly and continuously convert the parallel 8-bitdigital byte from the LUTs 68-1 through 68-6 to the input of the summingamplifier 72. The summing amplifier 72 is a conventional configurationof a circuit using an operational amplifier to linearly add severalindividual analog signals together to produce one composite signal.

A demodulation technique according to the present invention detects themodulated carrier and examines it to determine whether the sinusoidalfunction of the carrier has been altered at an interval Δθ followingeach phase angle θ_(n). For, example, if the carrier has been modulatedby maintaining the amplitude Y=sin θ_(n) for a short interval Δθfollowing the phase angle θ_(n), the modulated carrier is examined todetermine if Y=sin θ_(n) during the interval Δθ following the phaseangle θ_(n) or whether the amplitude has been following the functionY=sin θduring the interval Δθ following each phase angle θ_(n). Suchexamination may be accomplished, for example, by mixing the detectedsinusoidal carrier with a reference sinusoidal signal having the samefrequency and phase as the carrier to detect phase differences betweenthe reference sinusoidal signal and the modulated carrier, or byperforming fast fourier transform (FFT) analysis on the modulatedcarrier. Such a demodulator may also contain circuitry to detect“out-of-position” bits disposed in one or more of the carriers.

FIG. 6 is a block diagram of an illustrative demodulator circuit forextracting the information from a modulated sinusoidal carrier accordingto the techniques of the present invention. First, the incomingmodulated sinusoidal carrier is presented to signal input conditioningblock 80. The nature of the circuitry inside signal input conditioningblock 80 will depend upon the transmission medium used in thecommunication channel. For example, if the transmission medium is atwisted pair cable such as would be encountered in a telephone network,signal input conditioning block 80 may be formed from a differentialline receiver. If the transmission medium is a radio or microwavetransmitter, as may be encountered in a wireless or satellitecommunications system, the signal input conditioning block 80 mayconsist of the usual RF and IF front end circuitry, including antennas,RF amplifiers, down converters, and RF detectors if applicable to the RFsystem used.

The output of signal input conditioning block 80 is presented to narrowbandpass filter 82. Narrow bandpass filter 82 should have a Q of aboutat least 100. The center frequency of narrow bandpass filter 82 isselected to be the frequency of the modulated sinusoidal carrier. Thesignal from the narrow bandpass filter 82 is amplified in amplifier 84and presented to one side of double-balanced mixer 86. The other side ofdouble-balanced mixer 86 is fed by the output of numerically-controlledoscillator (NCO) 88. The frequency and phase of NCO 88 is set to thefrequency and phase of the one of the modulated sine waves within thepassband of bandpass filter 82.

In a communications system according to the present invention thatemploys a plurality of modulated carriers within a communicationschannel, provision is made for separately demodulating each of thecarriers to extract the encoded data. Referring now to FIG. 7, a blockdiagram shows an input line 90 driving a plurality of a plurality ofillustrative balanced mixers 92, 94, 96, 98, 80, and 82. Six balancedmixers are shown in FIG. 7, but persons of ordinary skill in the artwill readily understand that any number of balanced mixers could be useddepending on how many different-frequency modulated sinewaves weregenerated by the modulator circuitry of FIG. 5A.

Balanced mixers 92, 94, 96, 98, 100, and 102 are also driven from theoutputs of NCO multi-sine wave generator 104. Each output is a sinewaveform at one of the frequencies of the sinewave-modulated carriersfrom which the digitally encoded information is to be extracted. Theoutputs of balanced mixers 92, 94, 96, 98, 100, and 102 are combinedinto a serial or parallel output data stream in data convoluter 106according to known techniques.

Data convoluter 106 reassembles the digital data from the individualmodulated sinewaves. Because the individual modulated sinewaves are atdifferent frequencies, the n bits of data from each are arriving atdifferent rates. For example, in a system using telephone-line bandwidthbelow 3 KHz, the carrier frequencies might be 1 KHz, 1.2 KHz, 1.4 KHz .. . 3 KHz. The data in the 1 Khz carrier is arriving at a rate of n bitsper 1 mSec. The data in the 3 Khz carrier is arriving at three timesthat rate. Reassembly of the data from the different carriers is notmuch different from reassembling packet data in an IP packet network.Various known techniques can be employed. Persons of ordinary skill inthe art will understand that the details of the reassembly process willvary as a function of the manner in which the data was divided among theseveral carriers in a multi-carrier system.

According to one aspect of the invention, one carrier could be employedto carry control information necessary for one or more aspects of thecommunication, or a combination of control information and data.Depending on the amount of control information required in acommunications channel, the control information may be encoded in thecarrier having the lowest data rate (i.e., 1 KHz carrier in the exampleabove), the highest data rate (i.e., 3 KHz carrier in the exampleabove), or in one of the other carriers.

Referring now to FIG. 8, an alternate circuit and method fordemodulating a sinusoidal carrier modulated according to the principlesof the present invention is shown. This demodulator operates by drivinga moving dot LED display, where the illuminated dot represents the levelof the received modulated sinewave. Because the voltage of theunmodulated portions of the sinewave carrier and portions of the carriermodulated with a zero bit (such as shown at phase angle θ₄ of FIG. 1A),changes fairly rapidly while the voltage level at portions of thecarrier modulated with a one bit (such as shown at phase angle θ₄ ofFIG. 1A) stays constant for a longer period, the LED corresponding tothe voltage level starting at phase angle θ₄ of FIG. 1A will be brighterfor a longer time. This difference in brightness is sensed and decoded.

The demodulator circuit of FIG. 8 inputs one of the modulated sinewavesto a logic and LED driver circuit 110. In one embodiment of theinvention logic and LED driver circuit 110 may be a dot bar displayintegrated circuit such as a LM 3914 integrated circuit available fromNational Semiconductor Corporation of Santa Clara, Calif. The LM3914 isa monolithic integrated circuit that senses analog voltage levels andhas outputs for driving a plurality of LEDs, thus providing a linearanalog display. The display can be configured as a moving dot display.The outputs of logic and LED driver circuit 110 are shown driving fiveoptoisolator circuits 112-1 through 112-5. Each opto-isolator circuitcontains a LED optically coupled to a phototransistor. The LED has itsanode coupled to a positive potential and its cathode coupled to one ofthe outputs of the logic and LED driver circuit 110. The emitters of thephototransistors are shown grounded in FIG. 8 and the collectors arecoupled together and coupled to a positive voltage potential throughresistor 114, although persons of ordinary skill in the art willappreciate that other circuit configurations could be employed.

The difference between a “zero” bit and a “one” bit is a lower voltageat the bottom of resistor 114 for a “one” bit due to the higher currentdrawn by the one of the phototransistors that is conducting. The timingof the voltage level to determine which bit is being sensed is easilyderived from the available voltage, phase, and frame informationavailable in the particular system.

Persons of ordinary skill in the art will appreciate that theconfiguration of FIG. 8 will operate over a wide frequency range andthat care should be taken in selecting components for such a circuitintended for use at higher frequencies to ensure that their responsetimes are adequate for the frequency of intended use.

One communications system according to the present invention employs amodulator to insert at least one modulated carrier according to thepresent invention onto one end of a telephone line or other wire-paircommunications line. Preferably, a plurality of such modulated carriers,separated in frequency by a guard-band amount, are injected into theline. A demodulator is coupled to the other end of the telephone line orother wire-pair communications line. According to one embodiment of theinvention, a modulator and the demodulator may be located at each end ofthe line and the communications may be -two-way communications.According to another embodiment of the invention, the modulator and thedemodulator may negotiate a bit rate to be used in the communications.

Referring now to FIGS. 9A and 9B, block diagrams illustrate a two-waycommunications system 120 according to the present invention employing awire line as a communications medium. FIG. 9A shows a communicationssystem according to the present invention using a telephone line orother wire-pair communications line as the communications medium. Userstations 122-1 and 122-2 include an input device 124-1 and 124-2 (suchas a computer), respectively. Persons of ordinary skill in the art willappreciate that one of the user stations 122-1 and 122-2 may be aprovider such as an internet service provider (ISP), and that many userstations may connect to a single ISP as is known in the art.

Each station also includes a modulator/demodulator andI/O-signal-conditioning unit 126-1 and 126-2, respectively. Themodulator/demodulator may be configured as disclosed herein. As will beunderstood by persons of ordinary skill in the art, theI/O-signal-conditioning unit serves to prepare the modulated signals forsending over wire pair communications lines 128 to a telco centraloffice 130 as is known in the art.

Referring now to FIG. 9B, shows a communications system 140 according tothe present invention using broadband-over-power-line (BPL) technologyemploying electrical power line as the communications medium. Userstations 142-1 and 142-2 include an input device 144-1 and 144-2 (suchas a computer), respectively. Persons of ordinary skill in the art willappreciate that each of the user stations 142-1 and 142-2 maycommunicate with each other point-to-point or may be user stations orservers in a local-area network (LAN) environment including other userstations (not shown).

Each station also includes a modulator/demodulator andI/O-signal-conditioning unit 146-1 and 146-2, respectively. Themodulator/demodulator may be configured as disclosed herein. As will beunderstood by persons of ordinary skill in the art, theI/O-signal-conditioning unit serves to couple the user stations toelectrical outlets in a business or residence to transmit and receivethe modulated signals over electrical power lines 148 that are fed(through step-down transformers) to a 4.8 KV distribution transformer150 as is known in the art. Data going to or coming from locationsoutside of the distribution tree served by distribution transformer 150may be coupled into and out of distribution transformer 150 over, forexample fiber-optic cable 152 through I/O coupling circuit 154 as isknown in the BPL art. Fiber-optic cable 152 may be coupled to an ISP orother server entity as is known in the communications art.

Another communications system according to the present invention employsa modulator to insert at least one modulated carrier according to thepresent invention onto one end of a coaxial-cable communications line.The modulated carriers may be up-converted in frequency prior to beinginserted onto the coaxial cable line. Preferably, a plurality of suchmodulated carriers, separated in frequency by a guard-band amount, areinserted into the line. A demodulator is coupled to the other end of thecoaxial cable communications line. According to one embodiment of theinvention, a modulator and the demodulator may be located at each end ofthe line and the communications may be two-way communications. Accordingto another embodiment of the invention, the modulator and thedemodulator may negotiate a bit rate to be used in the communications.This aspect of the present invention is shown diagrammatically in FIG.10.

Referring now to FIG. 10, a block diagram illustrates a two-waycommunications system 160 according to the present invention employing acoaxial-cable communications line, such as may be found in a cabletelevision (CATV) system, as the communications medium. User stations162-1 and 162-2 include an input device 164-1 and 164-2 (such as acomputer), respectively. Persons of ordinary skill in the art willappreciate that one of the user stations 162-1 and 162-2 may be aprovider such as an internet service provider (ISP).

Each station also includes a modulator/demodulator andI/O-signal-conditioning unit 166-1 and 166-2, respectively. Themodulator/demodulator may be configured as disclosed herein. As will beunderstood by persons of ordinary skill in the art, theI/O-signal-conditioning unit serves to prepare the modulated signals forsending over coaxial-cable communications lines 168 to a CATV head end170 as is known in the art

Another communications system according to the present invention employsa modulator to generate at least one modulated carrier according to thepresent invention and to further modulate a radio-frequency (RF) carrierwith the at least one modulated carrier to form a wireless RF signal.The modulated carriers may be up-converted in frequency prior to beingRF modulated. Preferably, a plurality of such modulated carriers,separated in frequency by a guard-band amount, are RF modulated. The RFmodulated signal is then transmitted. The transmitted RF-modulatedsignal is then detected by a terrestrial RF receiver. A demodulator iscoupled to the terrestrial RF receiver. According to one embodiment ofthe invention, the communications may be two-way communications.According to another embodiment of the invention, the modulator and thedemodulator may negotiate a bit rate to be used in the communications.This aspect of the present invention is shown diagrammatically in FIG.11.

Referring now to FIG. 11, a block diagram illustrates a two-waycommunications system 180 according to the present invention employing aterrestrial RF wireless communications line as the communicationsmedium. User stations 182-1 and 182-2 include an input device 184-1 and184-2 (such as a computer), respectively. Persons of ordinary skill inthe art will appreciate that one of the user stations 182-1 and 182-2may be a provider such as an internet service provider (ISP).

Each station also includes a modulator/demodulator andI/O-signal-conditioning unit 186-1 and 186-2, respectively. Themodulator/demodulator may be configured as disclosed herein. As will beunderstood by persons of ordinary skill in the art, theI/O-signal-conditioning unit serves to prepare the modulated signals forwireless transmitting and receiving as is known in the art. RFtransceivers 188-1 and 188-2 are used to RF modulate and transmit themodulated sinusoidal carriers as well as receive and demodulate the RFsignals transmitted from the other station. Such RF equipment is wellknown in the RF transmitting and receiving art. As used herein, the term“RF” is intended to encompass the frequency spectrum between about 500KHz up to and including VHF and UHF portion of the frequency spectrum aswell as the microwave portion of the frequency spectrum.

Yet another communications system according to the present inventionemploys a modulator to generate at least one modulated carrier accordingto the present invention and to further modulate a radio-frequency (RF)carrier with the at least one modulated carrier to form a wireless RFsignal. The modulated carriers may be up-converted in frequency prior tobeing RF modulated. Preferably, a plurality of such modulated carriers,separated in frequency by a guard-band amount, are RF modulated. The RFmodulated signal is then transmitted to an earth-orbiting or othersatellite or spacecraft. A demodulator is coupled to the RF receiver inthe earth-orbiting or other satellite or spacecraft. The earth-orbitingor other satellite or spacecraft may then retransmit the RF signal toanother RF receiver or may demodulate it for local use. According to oneembodiment of the invention, the communications may be two-waycommunications. According to another embodiment of the invention, themodulator and the demodulator may negotiate a bit rate to be used in thecommunications. This aspect of the present invention is showndiagrammatically in FIG. 12.

Referring now to FIG. 12, a block diagram illustrates a two-waycommunications system 190 according to the present invention employing asatellite wireless communications line as the communications medium.User stations 192-1 and 192-2 include an input device 194-1 and 194-2(such as a computer), respectively. Persons of ordinary skill in the artwill appreciate that one of the user stations 192-1 and 192-2 may be aprovider such as an internet service provider (ISP).

Each station also includes a modulator/demodulator andI/O-signal-conditioning unit 196-1 and 196-2, respectively. Themodulator/demodulator may be configured as disclosed herein. As will beunderstood by persons of ordinary skill in the art, theI/O-signal-conditioning unit serves to prepare the modulated signals forwireless transmitting and receiving as is known in the art. Satellitestations 198-1 and 198-2 are used to microwave modulate and transmit themodulated sinusoidal carriers to satellite 200 as well as receive anddemodulate the microwave signals transmitted from the other station viasatellite 200. Such satellite equipment is well known in the microwavetransmitting and receiving art.

As previously disclosed, the modulator and demodulator circuits shown inFIGS. 3 through 8 are only illustrative and other modulating anddemodulating solutions are contemplated within the scope of the presentinvention. Persons of ordinary skill in the art will understand thatdigital signal processing techniques may be used in a communicationssystem according to the present invention to produce at least onemodulated sinusoidal carrier as shown in FIG. 2 and to demodulate the atleast one sinusoidal carrier. Such DSP modulators and demodulators areshown in FIGS. 13 and 14, respectively.

The Fast Fourier Transform (FFT) a mathematical method of convertingsignals in the time domain to representations in the frequency domain.An Inverse Fast Fourier Transform (IFFT) reverses the process by takingfrequency coefficients in the form of parallel digital data andconverting them back to a continuous periodic signal in the time domain.The IFFT can be used to generate the modulated sinewave signalsaccording to the present invention, and the FFT can be used todemodulate the modulated sinewave signals in accordance with the presentinvention. As will be appreciated by persons of ordinary skill in theart, the FFT and IFFT techniques for demodulation and modulationaccording to the present invention are useful up to frequencies wherethe processing engine clock speeds and A/D and D/A conversion speeds areabout 6 times the frequency of the highest frequency modulated sinewavecarrier to be modulated or demodulated.

Referring now to FIG. 13, frequency coefficients are presented to IFFTblock 210. Known DSP techniques are used to configure IFFT block 210.The IFFT modulates the digital representation of each audio carrier intothe precise elemental phase shifted signals required. The time domaindata output from IFFT block 210 is then fed to a Digital to Analog (D/A)converter 212 to create a time domain signal. Typical resolution for theIFFT block 210 and the D/A converter 212 is more than about 8 bits. TheD/A converter 214 should be fast enough to perform at least 100Kconversions per second

The output of the D/A converter is filtered by low-pass filter 214.Filtering of the output signal is constrained to removing the highfrequency noise without impairing the information content of eachcarrier. To this end, low-pass filter 214 may be implemented, forexample, as a 6-pole butterworth filter or as a zero-group-delayrealization with 60 dB/octave rolloff.

Referring now to FIG. 14, a FFT DSP embodiment of a demodulator circuitaccording to the present invention is disclosed.

Referring now to FIG. 15, a block diagram illustrates how acommunications system according to the present invention can be used inconjunction with an existing modem protocol. While FIG. 15 shows such asystem 220 using V.90 modem protocol, persons of ordinary skill in theart examining FI. 15 and the accompanying disclosure will appreciatethat other modem protocols could be integrated into the presentinvention.

Phone hybrid 222 provides an interface between the modem and thephysical telephone network. The hybrid also provides isolation betweenthe transmit and receive sides of the modem to enhance operation bymatching impedances and reducing the noise contribution in the receiverby the local transmitter.

A switch 224 diverts the connection of the hybrid to either the standardV.90 modem 226 or the multi-frequency modem configured from theremainder of the elements of FIG. 15. The state of the switch is underthe control of the microcontroller 228. The microcontroller 228 controlsthe overall operation of the system. It is a self-containedmicro-processing unit which includes RAM, ROM and a CPU. It provides theinterface between the 10/100 Ethernet or Universal Serial Bus (USB) 230and either the V.90 modem 226 or the multi-frequency modem configuredfrom the remainder of the elements of FIG. 15. The V.90 modem is astandard “56K” modem well known in the art. The V.90 modem provides theability for the modem to communicate at a standard low speed prior toswitching over to the high speed link provided by the unit describedabove.

The microcontroller 228 also commands and controls the interface to theIFFT and FFT blocks 232 and 234. The microcontroller 234 receives thedata from the 10/100 and USB bus 230 and formats it to the appropriateoutput to the IFFT 232 to generate the necessary signals for outputtingto the phone line. The microcontroller 228 also receives digital wordsfrom the FFT block 234 and interprets these digital words for datacontent before passing them on to 10/100 and USB bus 230. The systemclock for microcontroller is provided by the timing generator 236. Thetiming generator 236 provides clocks and system synchronization forsystem operation

The Inverse Fast Fourier Transform (IFFT) block 232 is a digital signalprocessing (DSP) process that converts digital words representative of asignal in the frequency domain to a signal in the time domain. Digitalword(s) representing frequency domain parameters are fed in parallel tothe IFFT 232. The IFFT 232 outputs a sequential stream of paralleldigital words representative of the analog signals to be produced in thetime domain. That data stream from the IFFT 232 is fed to a D/Aconverter 238 which turns the sequence of parallel digital data to asequence of analog levels producing, over time, a continuous analogsignal representative of the frequency parameters inputted to the IFFT232. The conversion clock and synchronization of the IFFT conversion isprovided by the timing generator 236.

The 16-bit D/A converter 238 linearly and continuously converts theparallel 16-bit digital word from the output of the Inverse Fast FourierTransform (IFFT) 234 block to a representative analog level. Thecontinuous sequential stream of analog output samples produce, overtime, a composite output analog signal which is fed through the switch204 and the hybrid 202 to the phone line. The sample rate forconstructing the analog signal is determined by the timing generator236.

A 16 bit A/D block 240 linearly converts the analog output from thehybrid 202 through the switch 204 to 16-bit digital words which arerepresentations of each sampled analog level. The 16-bit samples are fedin parallel to the input of the Fast Fourier Transform (FFT) 234. Thesample rate of the analog signals to the digital words is determined bythe timing generator 236.

The Fourier Transform (FFT) 234 is a digital signal processing (DSP)process that converts analog signals in the time domain to a digitalrepresentation of the signal in the frequency domain. Digital wordsrepresenting time domain samples from the A/D converter 240 are fed inparallel to the FFT 234. The FFT 234 subsequently outputs to themicrocontroller 208, parallel digital word(s) which are representativeof the frequency components of the sampled time domain (analog) signal.The conversion clock and synchronization of the FFT conversion isprovided by the timing generator 238.

The system 200 negotiates a connection using the V.90 modem. If theother station indicates that it can communicate using the techniques ofthe present invention, the microcontroller 208 causes switch 204 toconnect the D/A converter 238 and the A/D converter 240 to the hybridinstead of the V.90 modem.

Referring now to FIG. 16, a block diagram depicts an illustrative of amulti-frequency sinewave receiver 250. This drawing and associateddescription is for the reception of one of many carriers used in amulti-frequency system. An actual system would have several of thesereceivers working together on different frequencies to transfer vastamounts of data using this modulation technique.

Preamplifier 252 amplifies the incoming signal to compensate for theinsertion loss of the band pass filter 254. Band pass filter 254 filtersthe signal to reduce out-of-band interference. Post amplifier 256amplifies the filtered signal to compensate for the insertion loss ofthe Bandpass filter 254 and raises the signal level to that needed bythe balanced mixer 258.

A double balanced mixer 268 mixes the incoming signal with the output ofa local oscillator producing the sum and difference of the two signals.The local oscillator may be formed from a zero crossing detector thatproduces an output when the incoming signal crosses the zero-volt level.The zero crossing detector is used to generate the reference for thecarrier regenerator 262 that acts as the local oscillator and the phaselock loop 264 which generates the data clock. The carrier regeneratortakes the output of the zero crossing detector and creates a localoscillator output which is the same frequency and phase of that of theincoming signal. Phase locked loop 264 uses the output of the zerocrossing detector to generate a high frequency clock used to clock theretrieved data at the output of the comparator.

Low pass filter 266 removes the sum frequency component form the outputof the mixer 258, leaving the difference component which isrepresentative of the absolute phase difference between the input signaland the reference signal out of the local oscillator. Comparator 268compares the difference signal from the mixer to a fixed referenceproducing an output when the input signal is higher than the referencesignal. An output indicates there is a phase difference between inputand local oscillator indicating the presence of a data bit of value“one”.

Clock alignment block 270 under the control of the microcontroller 272aligns the data clock through a variable delay circuit. Using aprioriknowledge of where in the phase of the signal where the data bits arethis circuit filters out data clock pulses which are not in alignmentwith known valid data bits coming out of the comparator. The data isclocked into the multi-stage shift register 274 that is used as agathering repository for the data bits clocked in from the output of thecomparator 268. Microcontroller 272 is a preprogrammed device whichmonitors and controls the operation of the receiver. Microcontroller 272transfers the received data stored in the shift register out to otherareas.

Microcontroller 272 also detects “out-of-position” bits and reportstheir detection as an event that may be used by the system as disclosedherein.

While the invention has been described with reference to an exemplaryembodiment, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention.

1. A method for generating a substantially sinusoidal waveformcontaining encoded digital data having one of a first value and a secondvalue at selected phase angles θ_(n) comprising: generating the waveformhaving an amplitude Y defined by a first function at phase angles lyingoutside of regions having a range of Δθ beginning at each phase angleθ_(n), said first function being Y=sin θ; generating the waveform havingan amplitude Y defined by said first function at phase angles lyinginside said regions having a range of Δθ beginning at each phase angleθ_(n) where data of the first value is to be encoded; and generating thewaveform having an amplitude Y defined by a second function at phaseangles lying inside said regions having a range of Δθ associated witheach phase angle θ_(n) where data of the second value is to be encoded,said second function being different from Y=sin θ.
 2. The method ofclaim 1 wherein the number of selected phase angles θ_(n) is variable.3. The method of claim 1 wherein the number of selected phase anglesθ_(n) is dynamically variable during a communication in response tofeedback from an apparatus receiving said waveform.
 4. The method ofclaim 1 wherein the number of selected phase angles θ_(n) is dynamicallyvariable during a communication in response to negotiation with anapparatus receiving said waveform.
 5. The method of claim 1 wherein thevalue of each of said selected phase angles θ_(n) is variable.
 6. Themethod of claim 1 wherein the value of at least one of said selectedphase angles θ_(n), is altered for an interval of time to identify anevent.
 7. The method of claim 1 wherein the value of at least one ofsaid selected phase angles θ_(n) is altered for an interval of time toencode an additional data bit.
 8. A method for generating asubstantially sinusoidal waveform 1 containing encoded digital datahaving one of a first value and a second value at selected phase anglesθ_(n) comprising: generating the waveform having an amplitude Y definedby a first function at phase angles lying outside of regions having arange of Δθ beginning at each phase angle θ_(n), said first functionbeing Y=sin θ; generating the waveform having an amplitude Y defined bysaid first function at phase angles lying inside said regions having arange of Δθ beginning at each phase angle θ_(n) where data of the firstvalue is to be encoded; and generating the waveform having an amplitudeY defined by a second function at phase angles lying inside said regionshaving a range of Δθ associated with each phase angle θ_(n) where dataof the second value is to be encoded, said second function being one ofY=sin θ_(n) and Y=sin θ_((n+Δθ)).
 9. The method of claim 8 wherein thenumber of selected phase angles θ_(n) is variable.
 10. The method ofclaim 8 wherein the number of selected phase angles θ_(n) is dynamicallyvariable during a communication in response to feedback from anapparatus receiving said waveform.
 11. The method of claim 8 wherein thenumber of selected phase angles θ_(n) is dynamically variable during acommunication in response to negotiation with an apparatus receivingsaid waveform.
 12. The method of claim 8 wherein the value of at leastone of said selected phase angles θ_(n) is variable.
 13. The method ofclaim 8 wherein the value of at least one of said selected phase anglesθ_(n) is altered for an interval of time to identify an event.
 14. Themethod of claim 8 wherein the value of at least one of said selectedphase angles θ_(n) is altered for an interval of time to encode anadditional data bit.
 15. A method for generating a plurality ofsubstantially sinusoidal waveforms each having a different frequency andcontaining encoded digital data having one of a first value and a secondvalue at selected phase angles θ_(n) comprising: generating eachwaveform having an amplitude Y defined by a first function at phaseangles lying outside of regions having a range of Δθ beginning at eachphase angle θ_(n), said first function being Y=sin θ; generating eachwaveform having an amplitude Y defined by said first function at phaseangles lying inside said regions having a range of Δθ beginning at eachphase angle θ_(n) where data of the first value is to be encoded; andgenerating each waveform having an amplitude Y defined by a secondfunction at phase angles lying inside said regions having a range of Δθassociated with each phase angle θ_(n) where data of the second value isto be encoded, said second function being different from Y=sin θ. 16.The method of claim 15 wherein the number of selected phase angles θ_(n)for each waveform is variable.
 17. The method of claim 15 wherein thenumber of selected phase angles θ_(n) for each waveform is dynamicallyvariable during a communication in response to feedback from anapparatus receiving said each waveform.
 18. The method of claim 15wherein the number of selected phase angles θ_(n) for each waveform isdynamically variable during a communication in response to negotiationwith an apparatus receiving said each waveform.
 19. The method of claim15 wherein the value of at least one of said selected phase angles θ_(n)in at least one of said waveforms is altered for an interval of time toidentify an event.
 20. The method of claim 15 wherein the value of atleast one of said selected phase angles θ_(n) in at least one of saidwaveforms is altered for an interval of time to encode an additionaldata bit.
 21. A method for generating a plurality of substantiallysinusoidal waveforms each having a different frequency and containingencoded digital data having one of a first value and a second value atselected phase angles θ_(n) comprising: generating each waveform havingan amplitude Y defined by a first function at phase angles lying outsideof regions having a range of Δθ beginning at each phase angle θ_(n),said first function being Y=sin θ; generating each waveform having anamplitude Y defined by said first function at phase angles lying insidesaid regions having a range of Δθ beginning at each phase angle θ_(n)where data of the first value is to be encoded; and generating eachwaveform having an amplitude Y defined by a second function at phaseangles lying inside said regions having a range of Δθ associated witheach phase angle θ_(n) where data of the second value is to be encoded,said second function being one of Y=sin θ_(n), and Y=sin θ_((n+Δθ)). 22.The method of claim 21 wherein the number of selected phase angles θ_(n)for each waveform is variable.
 23. The method of claim 21 wherein thenumber of selected phase angles θ_(n) for each waveform is dynamicallyvariable during a communication in response to feedback from anapparatus receiving said each waveform.
 24. The method of claim 21wherein the number of selected phase angles θ_(n) for each waveform isdynamically variable during a communication in response to negotiationwith an apparatus receiving said each waveform.
 25. The method of claim21 wherein the value of at least one of said selected phase angles θ_(n)in at least one of said waveforms is altered for an interval of time toidentify an event.
 26. The method of claim 21 wherein the value of atleast one of said selected phase angles θ_(n) in at least one of saidwaveforms is altered for an interval of time to encode an additionaldata bit.
 27. A method for decoding information from a substantiallysinusoidal waveform containing encoded digital data at selected phaseangles θ_(n), the waveform having an amplitude Y=sin θ at phase angleslying outside of regions having a range of Δθ beginning at each phaseangle θ_(n), the waveform having an amplitude Y=sin θ at phase angleslying inside the regions having a range of Δθ beginning at each phaseangle On where data of the first value is to be encoded, the waveformhaving an amplitude Y defined by a different from Y=sin θ at phaseangles lying inside the regions having a range of Δθ associated witheach phase angle θ_(n) where data of the second value is to be encoded,comprising: receiving the sinusoidal waveform containing encoded digitaldata; generating a reference sinusoidal waveform from said substantiallysinusoidal waveform containing encoded digital data, said referencesinusoidal waveform having a constant phase relationship with saidsinusoidal waveform containing encoded digital data; mixing saidreference sinusoidal waveform and said substantially sinusoidal waveformcontaining encoded digital data in a balanced mixer; and extracting saidencoded digital data from said balanced mixer.
 28. A method for decodinginformation from a substantially sinusoidal waveform containing encodeddigital data at selected phase angles θ_(n), the waveform having anamplitude Y=sin θ at phase angles lying outside of regions having arange of Δθ beginning at each phase angle θ_(n), the waveform having anamplitude Y=sin θ at phase angles lying inside the regions having arange of Δθ beginning at each phase angle θ_(n) where data of the firstvalue is to be encoded, the waveform having an amplitude Y defined by adifferent from Y=sin θ at phase angles lying inside the regions having arange of Δθ associated with each phase angle θ_(n) where data of thesecond value is to be encoded, comprising: receiving the sinusoidalwaveform containing encoded digital data; digitizing said sinusoidalwaveform containing encoded digital data; generating a digital referencesinusoidal waveform having a constant phase relationship with saidsinusoidal waveform containing encoded digital data; and performinginverse fast fourier transform digital signal processing on saidreference sinusoidal waveform and said substantially sinusoidal waveformcontaining encoded digital data.
 29. A communications system forcommunicating in a communications medium and comprising: a first stationincluding: an encoder for generating at least one substantiallysinusoidal waveform containing encoded digital data at selected phaseangles θ_(n), the waveform having an amplitude Y=sin θ at phase angleslying outside of regions having a range of Δθ beginning at each phaseangle θ_(n), the waveform having an amplitude Y=sin θ at phase angleslying inside the regions having a range of Δθ beginning at each phaseangle θ_(n) where data of the first value is to be encoded, the waveformhaving an amplitude Y defined by a different from Y=sin θ at phaseangles lying inside the regions having a range of Δθ associated witheach phase angle θ_(n) where data of the second value is to be encoded;and a transmitter for transmitting said at least one substantiallysinusoidal waveform containing encoded digital data through said medium;a second station coupled to said first station through saidcommunications medium and including: a receiver for receiving said atleast one substantially sinusoidal waveform containing encoded digitaldata through said medium from said first station; and a decoder forextracting said digital data from said at least one substantiallysinusoidal waveform containing encoded digital data.
 30. Thecommunications system of claim 29 wherein said communications medium isa wire system.
 31. The communications system of claim 29 wherein saidcommunications medium is a telephone system.
 32. The communicationssystem of claim 29 wherein said communications medium is a powerdistribution system.
 33. The communications system of claim 29 whereinsaid communications medium is a coaxial cable.
 34. The communicationssystem of claim 33 wherein said communications medium is a cabletelevision system.
 35. The communications system of claim 29 whereinsaid communications medium is a terrestrial wireless channel.
 36. Thecommunications system of claim 35 wherein said communications medium isa radio frequency channel.
 37. The communications system of claim 35wherein said communications medium is a television channel.
 38. Thecommunications system of claim 29 wherein said communications medium isa microwave link.
 39. The communications system of claim 38 wherein saidfirst station is an earth station and said second station isextraterrestrial.
 40. The communications system of claim 39 wherein saidsecond station is on board a spacecraft.
 41. The communications systemof claim 39 wherein said second station is a satellite.
 42. Thecommunications system of claim 29 further including: a third stationpledto said second station through said communications medium and including:a receiver for receiving said substantially sinusoidal waveformcontaining encoded digital data through said medium; and a decoder forextracting said digital data from said substantially sinusoidal waveformcontaining encoded digital data and wherein said second station furtherincludes a transmitter for transmitting said substantially sinusoidalwaveform containing said encoded digital data through said medium tosaid third station.
 43. The method of claim 29 wherein the number ofselected phase angles θ_(n) for each waveform is variable.
 44. Themethod of claim 29 wherein the number of selected phase angles θ_(n) foreach waveform is dynamically variable during a communication in responseto feedback from a receiving apparatus receiving said each waveform. 45.The method of claim 29 wherein the number of selected phase angles θ_(n)for each waveform is dynamically variable during a communication inresponse to negotiation with a receiving apparatus receiving said eachwaveform.
 46. The method of claim 29 wherein the value of at least oneof said selected phase angles θ_(n) in at least one of said waveforms isaltered for an interval of time to identify an event.
 47. The method ofclaim 29 wherein the value of at least one of said selected phase anglesθ_(n) in at least one of said waveforms is altered for an interval oftime to encode an additional data bit.
 48. A communications system forcommunicating in a communications medium and comprising: a firststation; a second station coupled to said first station through saidcommunications medium: wherein said first and second stations eachinclude: an encoder for generating at least one substantially sinusoidalwaveform containing encoded digital data at selected phase angles θ_(n),the waveform having an amplitude Y=sin θ at phase angles lying outsideof regions having a range of Δθ beginning at each phase angle θ_(n), thewaveform having an amplitude Y=sin θ at phase angles lying inside theregions having a range of Δθ beginning at each phase angle θ_(n) wheredata of the first value is to be encoded, the waveform having anamplitude Y defined by a different from Y=sin θ at phase angles lyinginside the regions having a range of Δθ associated with each phase angleθ_(n) where data of the second value is to be encoded; a transmitter fortransmitting said at least one substantially sinusoidal waveformcontaining encoded digital data through said medium; a receiver forreceiving said at least one substantially sinusoidal waveform containingencoded digital data through said medium; and a decoder for extractingsaid digital data from said at least one substantially sinusoidalwaveform containing encoded digital data.
 49. The communications systemof claim 48 wherein said communications medium is a wire system.
 50. Thecommunications system of claim 48 wherein said communications medium isa telephone system.
 51. The communications system of claim 49 whereinsaid communications medium is a power distribution system.
 52. Thecommunications system of claim 48 wherein said communications medium isa coaxial cable.
 53. The communications system of claim 52 wherein saidcommunications medium is a cable television system.
 54. Thecommunications system of claim 48 wherein said communications medium isa terrestrial wireless channel.
 55. The communications system of claim54 wherein said communications medium is a radio frequency channel. 56.The communications system of claim 54 wherein said communications mediumis a television channel.
 57. The communications system of claim 54wherein said communications medium is a microwave link.
 58. Thecommunications system of claim 48 wherein said first station is an earthstation and said second station is extraterrestrial.
 59. Thecommunications system of claim 58 wherein said second station is onboard a spacecraft.
 60. The communications system of claim 58 whereinsaid second station is a satellite.
 61. The communications system ofclaim 48 further including: a third station coupled to said secondstation through said communications medium and including: a receiver forreceiving said substantially sinusoidal waveform containing encodeddigital data through said medium; and a decoder for extracting saiddigital data from said substantially sinusoidal waveform containingencoded digital data and wherein said second station further includes atransmitter for transmitting said substantially sinusoidal waveformcontaining encoded digital data through said medium to said thirdstation.
 62. The method of claim 48 wherein the number of selected phaseangles θ_(n) for each waveform is variable.
 63. The method of claim 48wherein the number of selected phase angles θ_(n) for each waveform isdynamically variable during a communication in response to feedback froma receiving apparatus receiving said each waveform.
 64. The method ofclaim 48 wherein the number of selected phase angles θ_(n) for eachwaveform is dynamically variable during a communication in response tonegotiation with a receiving apparatus receiving said each waveform. 65.The method of claim 48 wherein the value of at least one of saidselected phase angles θ_(n) in at least one of said waveforms is alteredfor an interval of time to identify an event.
 66. The method of claim 48wherein the value of at least one of said selected phase angles θ_(n) inat least one of said waveforms is altered for an interval of time toencode an additional data bit.
 67. Apparatus for generating asubstantially sinusoidal waveform containing encoded digital data havingone of a first value and a second value at selected phase angles θ_(n)comprising: means for generating the waveform having an amplitude Ydefined by a first function at phase angles lying outside of regionshaving a range of Δθ beginning at each phase angle θ_(n), said firstfunction being Y=sin θ, means for generating the waveform having anamplitude Y defined by said first function at phase angles lying insidesaid regions having a range of Δθ beginning at each phase angle θ_(n)where data of the first value is to be encoded; and means for generatingthe waveform having an amplitude Y defined by a second function at phaseangles lying inside said regions having a range of Δθ associated witheach phase angle θ_(n) where data of the second value is to be encoded,said second function being different from Y=sin θ.
 68. The apparatus ofclaim 67 further including means for changing the number of selectedphase angles θ_(n).
 69. The apparatus of claim 67 further includingmeans for dynamically varying the number of selected phase angles θ_(n)during a communication in response to feedback from an apparatusreceiving said waveform.
 70. The apparatus of claim 67 further includingmeans for dynamically varying the number of selected phase angles θ_(n)during a communication in response to negotiation with an apparatusreceiving said waveform.
 71. The apparatus of claim 67 further includingmeans for varying the value of each of said selected phase angles θ_(n).72. The apparatus of claim 67 further including means for altering thevalue of at least one of said selected phase angles θ_(n) for aninterval of time to identify an event.
 73. The apparatus of claim 67further including means for altering the value of at least one of saidselected phase angles θ_(n) for an interval of time to encode anadditional data bit.
 74. Apparatus for generating a substantiallysinusoidal waveform containing encoded digital data having one of afirst value and a second value at selected phase angles θ_(n)comprising: generating the waveform having an amplitude Y defined by afirst function at phase angles lying outside of regions having a rangeof Δθ beginning at each phase angle θ_(n), said first function beingY=sin θ; generating the waveform having an amplitude Y defined by saidfirst function at phase angles lying inside said regions having a rangeof Δθ beginning at each phase angle θ_(n) where data of the first valueis to be encoded; and generating the waveform having an amplitude Ydefined by a second function at phase angles lying inside said regionshaving a range of Δθ associated with each phase angle θ_(n) where dataof the second value is to be encoded, said second function being one ofY=sin θ_(n) and Y=sin θ_((n+Δθ)).
 75. The apparatus of claim 74 furtherincluding means for changing the number of selected phase angles θ_(n).76. The apparatus of claim 74 further including means for dynamicallyvarying the number of selected phase angles θ_(n) during a communicationin response to feedback from an apparatus receiving said waveform. 77.The apparatus of claim 74 further including means for dynamicallyvarying the number of selected phase angles θ_(n) during a communicationin response to negotiation with an apparatus receiving said waveform.78. The apparatus of claim 74 further including means for varying thevalue of each of said selected phase angles θ_(n).
 79. The apparatus ofclaim 74 further including means for altering the value of at least oneof said selected phase angles θ_(n) for an interval of time to identifyan event.
 80. The apparatus of claim 74 further including means foraltering the value of at least one of said selected phase angles θ_(n)for an interval of time to encode an additional data bit.